1. Field of the Invention
This invention relates to sequential data block address processing circuits for deriving address signals in dependence on incoming data which comprises sequential blocks of data each including an address signal. The invention is particularly, but not exclusively, for deriving address signals in dependence on incoming data derived from a digital video tape recorder (VTR), and which comprises sequential blocks of data each formed by a plurality of pulse coded samples together representing a block of video information.
2. Description of the Prior Art
Recently there has been an increasing interest in the use of digital techniques for television signals. Such techniques are, for example, used in some video tape recording arrangements where an incoming television signal to be recorded is sampled, the samples are pulse code modulation coded into digital form, the digital data signals are recorded and subsequently reproduced by a VTR, the reproduced digital data signals are decoded, and the decoded signals are used to form an analog signal which is a replica of the original television signal.
For the purpose of recording it is usual to divide the digital data signals into blocks and to associate with each block synchronizing and address signals for use in identifying and decoding the digital signals after reproduction. The decoding apparatus generally includds some form of address counter which, when it has been locked to the incoming addresses, is able to free-wheel over any subsequent gaps in the incoming addresses due, for example, to drop-out or corruption of the information being read off a magnetic tape. Before the address counter is locked onto the incoming addresses it is necessary to be as sure as possible that the incoming addresses are valid; otherwise the address counter may be incorrectly locked with consequent erroneous routing of incoming blocks of data. This will cause severe degradation of the resulting television picture which will continue until the address counter re-locks onto valid incoming addresses.